The present disclosure relates to techniques for performing formation evaluation. More particularly, the present disclosure relates to techniques, such as calibrations, that may be used in performing measurement, imaging and/or other formation evaluations.
To locate and capture valuable hydrocarbons from subterranean formations, various wellsite tools may be used to perform various tasks, such as drilling a wellbore, performing downhole testing and producing downhole fluids. Downhole drilling tools may be advanced into the earth by a drill string with a bit at an end thereof to form the wellbore. Drilling muds (or other drilling fluids) may be pumped into the wellbore and through the drilling tool as it advances into the earth. The drilling muds may be used, for example, to remove cuttings, to cool the drill bit and/or to provide a coating along the wellbore. The drilling muds may be conductive or non-conductive drilling fluids (e.g., oil based muds (OBM), water based muds (WBM), etc.) During or after drilling, casing may be cemented into place to line a portion of the wellbore, and production tools may be used to draw the downhole fluids to the surface.
During wellsite activities, downhole measurements may be taken to collect information about downhole conditions. The downhole measurements may be taken of various wellsite parameters, such as temperature, pressure, permittivity, impedance, resistivity, gain factor, button standoff, impedance phase offset, etc. Downhole tools, such as the drilling tool, a testing tool, a production tool, or other tools, may be deployed into the wellbore to take the downhole measurements, such as formation resistivity. These downhole measurements may be used to generate downhole parameters, such as impedance of electrodes used in taking the downhole measurements, vectors of the impedance, and the length of such vectors (e.g., Z90). In some cases, downhole logs, images or other outputs may be generated from the downhole measurements.